This invention relates generally to wireless communication systems.
Wireless communication has extensive applications in consumer and business markets. Among the many communication applications/systems are: mobile wireless, fixed wireless, unlicensed Federal Communications Commission (FCC) wireless, local area network (LAN), cordless telephony, personal base station, telemetry, and others.
Signal processing protocols and standards have proliferated with advances in wireless communications devices and services. Current communications protocols include Frequency Division Multiplexing (FDM), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). The United States, Europe, Japan, and Korea have all developed their own standards for each communications protocol. TDMA standards include Interim Standard-136 (IS-136), Global System for Mobile (GSM), and General Packet Radio Service (GPRS). CDMA standards include Global Positioning System (GPS), Interim Standard-95 (IS-95) and Wide Band CDMA (WCDMA). Wireless communications services include paging, voice and data applications.
In many cases, within the same field of applications, different systems use incompatible modulation techniques and protocols. Consequently, each system may require unique hardware, software, and methodologies for baseband processing. This practice can be costly in terms of design, testing, manufacturing, and infrastructure resources. As a result, a need arises to overcome the limitations associated with the varied hardware, software, and methodology of processing digital signals in each of the varied applications.
Until recently, individual wireless communications devices supported a single communications standard. In theory, however, a wireless communications device can be designed using a general purpose Digital Signal Processor (DSP) that is programmed first to realize a first set of functional blocks specifying the minimum performance requirements for a first application and can be reprogrammed to realize a second set of functional blocks to provide a second application. To achieve these minimum performance requirements, system designers design algorithms (sequences of arithmetic, trigonometric, logic, control, memory access, indexing operations, and the like) to encode, transmit, and decode signals. These algorithms are typically specified in software. The set of algorithms which achieve the target performance specification is collectively referred to as the executable specification. This executable specification can then be compiled and run on the DSP, typically via the use of a compiler. Despite the increasing computational power and speed of general purpose DSPs and decreasing memory cost and size, designers have not been able to satisfy cost, power and speed requirements simply by programming a general purpose DSP with the executable specification for a standard-specific application.
Additional dedicated high-speed processing is required, a need which has traditionally been met using an application-specific processor. As used herein, an application-specific processor is a processor that excels in the efficient execution (power, area, flexibility) of a set of algorithms tailored to the application. An application-specific processor, however, fares extremely poorly for algorithms outside the intended application space. In other words, the improved speed and power efficiency of application-specific-processors comes at the cost of function flexibility.
Demand is now growing for wireless communications devices that support multiple applications and varying grades of services over multiple standards. In particular, demand is growing for cellular handsets, which are one type of wireless communications device, to support multiple applications and services over multiple standards. Today's solution to this problem is to essentially connect multiple application-specific processors together to obtain multi-standard operation, thereby adding cost in terms of design resources, design time, and silicon area.
Cellular handsets and basestations, including PCS (Personal Communications Services) and 3-G (Third Generation) devices, need to acquire certain cell specific information and characteristics before negotiating a service with a base station. For this purpose, each base station transmits certain cell specific information necessary for a user to acquire services such as paging or cellular telephony from the base station. For example, in CDMA based systems, the cell specific information is contained in pilot and/or synchronization channels. The pilot and/or synchronization channels are spread and scrambled with cell specific pseudo-random noise (PN) or gold code sequences. At the receiver, the scrambled sequence is converted back to the original data sequence.
Multiple users are typically served at a single base station. In CDMA systems, each user is assigned an orthogonal code from a set of orthogonal codes and data that is transmitted from the base station to the user is spread according to the assigned orthogonal code. Even though users operate on the same frequency at the same time, the use of orthogonal codes allow multiple users to be distinguished from one another.
Some data processing systems employ a generic time-sliced architecture to perform data processing functions. Typically, a user builds an application on top of a generic time-sliced architecture based on fixed constraints inherent in the generic time-sliced architecture. For example, data processing engines are designed to optimize the performance on the silicon process for a generic set of operations. When using a generic time-sliced architecture, a user designing an application has the responsibility of real time scheduling (e.g., reading and writing to and from memory) on the generic time sliced architecture. This responsibility is particularly burdensome if a high volume of data comes in at a very high speed, such as data arriving in wireless communications. In addition, even if a user is able to write applications that successfully schedule real time processes, the user still has the burden of managing and maintaining real time aspects of the processing at the lowest level (i.e., below radio frame).
In view of the foregoing, it is desirable to provide a specific processor that supports disparate communications and signal processing standards in a cost, area, and power efficient fashion. It is further desirable to provide a method and apparatus that automates time scheduling aspects of data processing by optimizing a specific time-sliced and multi-threaded architecture in a communication system.